feat(ReadOnlySequence): GetFirst interface and tests.

Author: aensidhe

src/msgpack.spec/MsgPackSpec.Exceptions.cs

@@ -13,10 +13,8 @@ namespace ProGaudi.MsgPack
     [PublicAPI]
     public static partial class MsgPackSpec
     {
-        private static Exception GetReadOnlySequenceIsTooShortException(int expected, long sequenceLength) => new ArgumentOutOfRangeException(
-            nameof(sequenceLength),
-            sequenceLength,
-            $"ReadOnlySequence is too short. Expected: {expected}"
+        private static Exception GetReadOnlySequenceIsTooShortException(int expected, long sequenceLength) => new IndexOutOfRangeException(
+            $"ReadOnlySequence is too short. Expected: {expected}, actual length: {sequenceLength}"
         );
 
         private static Exception GetInvalidStringException() => new InvalidOperationException(

src/msgpack.spec/MsgPackSpec.ExtensionMethods.cs

@@ -15,20 +15,20 @@ public static partial class MsgPackSpec
         /// <param name="ros">Sequence</param>
         /// <typeparam name="T">Type of elements</typeparam>
         /// <returns>First element of sequence.</returns>
-        /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="ros"/> is empty</exception>
+        /// <exception cref="IndexOutOfRangeException">Thrown when <paramref name="ros"/> is empty</exception>
+        /// <exception cref="InvalidOperationException">When <see cref="ReadOnlySequence{T}.IsEmpty"/> is <c>false</c>, but sequence is still empty.</exception>
         public static T GetFirst<T>(this ReadOnlySequence<T> ros)
         {
+            if (ros.IsEmpty) throw GetReadOnlySequenceIsTooShortException(1, 0);
             if (ros.IsSingleSegment) return ros.First.Span[0];
-            if (!ros.IsEmpty)
+
+            foreach (var memory in ros)
             {
-                foreach (var memory in ros)
-                {
-                    if (!memory.IsEmpty)
-                        return memory.Span[0];
-                }
+                if (!memory.IsEmpty)
+                    return memory.Span[0];
             }
 
-            throw GetReadOnlySequenceIsTooShortException(1, 0);
+            throw new InvalidOperationException("We should never get here, because it means that non-empty sequence is empty.")
         }
 
         /// <summary>
@@ -43,7 +43,7 @@ public static bool TryFillSpan<T>(this ReadOnlySequence<T> ros, Span<T> destinat
         {
             if (destination.IsEmpty) return true;
             if (ros.IsSingleSegment) return ros.First.Span.TryCopyTo(destination);
-            
+
             var span = destination;
             foreach (var memory in ros)
             {

tests/msgpack.spec.tests/ReadOnlySequence/MultipleSegments/GetFirst.cs

@@ -0,0 +1,39 @@
+using System;
+using Shouldly;
+using Xunit;
+
+namespace ProGaudi.MsgPack.Tests.ReadOnlySequence.MultipleSegments
+{
+    public class PublicExtensions
+    {
+        [Theory]
+        [InlineData(new byte[] {1})]
+        [InlineData(new byte[] {byte.MaxValue, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10})]
+        public void GetFirstByteNonEmpty(byte[] data)
+        {
+            data.ToMultipleSegments().GetFirst().ShouldBe(data[0]);
+        }
+
+        [Fact]
+        public void GetFirstByteEmpty()
+        {
+            var e = Should.Throw<IndexOutOfRangeException>(() => System.Array.Empty<byte>().ToMultipleSegments().GetFirst());
+            e.Message.ShouldBe("ReadOnlySequence is too short. Expected: 1, actual length: 0");
+        }
+
+        [Theory]
+        [InlineData(new[] {1})]
+        [InlineData(new[] {int.MaxValue, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10})]
+        public void GetFirstNonByteNonEmpty(int[] data)
+        {
+            data.ToMultipleSegments().GetFirst().ShouldBe(data[0]);
+        }
+
+        [Fact]
+        public void GetFirstNonByteEmpty()
+        {
+            var e = Should.Throw<IndexOutOfRangeException>(() => System.Array.Empty<byte>().ToMultipleSegments().GetFirst());
+            e.Message.ShouldBe("ReadOnlySequence is too short. Expected: 1, actual length: 0");
+        }
+    }
+}

tests/msgpack.spec.tests/ReadOnlySequence/SingleSegment/GetFirst.cs

@@ -0,0 +1,39 @@
+using System;
+using Shouldly;
+using Xunit;
+
+namespace ProGaudi.MsgPack.Tests.ReadOnlySequence.SingleSegment
+{
+    public class PublicExtensions
+    {
+        [Theory]
+        [InlineData(new byte[] {1})]
+        [InlineData(new byte[] {byte.MaxValue, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10})]
+        public void GetFirstByteNonEmpty(byte[] data)
+        {
+            data.ToSingleSegment().GetFirst().ShouldBe(data[0]);
+        }
+
+        [Fact]
+        public void GetFirstByteEmpty()
+        {
+            var e = Should.Throw<IndexOutOfRangeException>(() => System.Array.Empty<byte>().ToSingleSegment().GetFirst());
+            e.Message.ShouldBe("ReadOnlySequence is too short. Expected: 1, actual length: 0");
+        }
+
+        [Theory]
+        [InlineData(new[] {1})]
+        [InlineData(new[] {int.MaxValue, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10})]
+        public void GetFirstNonByteNonEmpty(int[] data)
+        {
+            data.ToSingleSegment().GetFirst().ShouldBe(data[0]);
+        }
+
+        [Fact]
+        public void GetFirstNonByteEmpty()
+        {
+            var e = Should.Throw<IndexOutOfRangeException>(() => System.Array.Empty<byte>().ToSingleSegment().GetFirst());
+            e.Message.ShouldBe("ReadOnlySequence is too short. Expected: 1, actual length: 0");
+        }
+    }
+}